Factors that Influence Diffusion (Cambridge (CIE) IGCSE Biology): Revision Note

Factors that influence diffusion

Surface area to volume ratio

• The bigger a cell or structure is, the smaller its surface area to volume ratio is, slowing down the rate at which substances can move across its surface

  • Bigger structures have proportionally less surface area relative to their volume, which limits diffusion efficiency

• Many cells which are adapted for diffusion have increased surface area in some way, for example:

  • root hair cells in plants (which absorb water and mineral ions)

  • cells lining the ileum in animals (which absorb the products of digestion)

Distance

• The smaller the distance molecules have to travel, the higher the rate at which diffusion can occur

• This is why blood capillaries and alveoli have walls which are only one cell thick, to ensure the rate of diffusion across them is as high as possible

Temperature

• The higher the temperature, the faster molecules move as they have more kinetic energy

• There is therefore a faster net rate of diffusion of molecules from a high to low concentration at higher temperatures

Concentration gradient

• The greater the difference in concentration on either side of the membrane, the greater the rate of diffusion

• This is because there are more molecules on the higher-concentration side, so more molecules move from high to low concentration by random motion than move from low to high - giving a faster net rate of diffusion in that direction